This invention relates to reciprocating expansion engines for cryogenic refrigeration. In particular, this invention is useful as an improvement in an existing cryogenic piston refrigeration system that is the subject of U.S. patent application Ser. No. 740,330, allowed but not issued as of the present date. The reciprocating expansion engine that is the subject of that patent application is adaptable for use either as part of a refrigerator or as part if a liquifier in cryogenic applications, depending upon the mode of operation. In either case, the operating parts are exposed to temperature extremes when the working fluid is one such as helium which must be handled at temperatures of the order of a few K. The refrigerator or liquefier disclosed in U.S. application Ser. No. 740,330 worked as an expander for a cryogenic refrigerator or liquefier, but it required a considerable amount of effort to find an optimum sealing arrangement for the pistons. In order to maximize the efficiency of an expander, it is necessary to minimize both blow-by and friction heating of the piston ring. Excessive tightness of the piston ring in the cylinder causes excessive friction heating, while insufficient tightness of the piston ring in the cylinder causes excessive blow-by. It was difficult to achieve a workable seal since no method was provided for controlling tightness of the piston ring in the cylinder. This operation could have been improved by a system making it possible to adjust the sealing to permit an optimum amount of blow-by of the cryogenic fluid, enough to reduce sliding friction without producing excessive loss of efficiency.
It is an object of the present invention to provide a better method of sealing a piston of a reciprocating cryogenic refrigerator or liquefier.
It is a further object of the present invention to provide a means of varying the seal between a piston and a cylinder of a reciprocating cryogenic refrigerator or liquefier while the machine is operating.
It is a further object of the present invention to provide a means of adjusting the seal between the piston and cylinder of a reciprocating cryogenic refrigerator or liquefier in response to a sensor to permit the optimum amount of blow-by of the cryogenic fluid.
Other objects will become apparent in the course of a detailed description of the invention.